A head up display emits light that reflects from the front windshield to be seen by the driver. The light appears to come from a virtual image in front of the driver and in front of the windshield. This type of head up display is currently commercially available.
Conventional head up displays create the virtual image by first using a display to create an image. Next, the light from the image is reflected from one or more mirrors. Next, the light from the mirrors is reflected from the windshield. The mirrors are designed and positioned relative to the display so that the light seen by the driver, which is reflected from the windshield, appears to come from a virtual image that is outside of the vehicle. The mirrors and display are typically contained in a package that occupies a volume beneath the top surface of the dashboard.
Many current owners of HUD-equipped vehicles have expressed unhappiness with inability to view the HUD image while wearing polarized sunglasses. The following methods are known to enable the image of a windshield HUD to be viewed with polarized sunglasses: (1) The HUD projector emits circularly polarized or elliptically polarized light. This is not a fully satisfactory solution since the windshield reflectivity to p-polarized light is small; (2) The driver can wear non-polarizing sunglasses; (3) A plastic lens, including a wave plate, can be clipped over the polarizing sunglasses; and (4) An interior surface of the windshield can be coated with a reflective layer. Doing so increases windshield reflectance, and, as a result, increases veiling glare.